EP0599375B1 - Light modulator - Google Patents

Light modulator Download PDF

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Publication number
EP0599375B1
EP0599375B1 EP93203160A EP93203160A EP0599375B1 EP 0599375 B1 EP0599375 B1 EP 0599375B1 EP 93203160 A EP93203160 A EP 93203160A EP 93203160 A EP93203160 A EP 93203160A EP 0599375 B1 EP0599375 B1 EP 0599375B1
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EP
European Patent Office
Prior art keywords
partial
mirrors
partial mirrors
optical fibre
optical
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EP93203160A
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German (de)
French (fr)
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EP0599375A1 (en
Inventor
Paul Dr. Vogel
Rainer Bättig
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Ascom Tech AG
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Ascom Tech AG
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J3/26—Generating the spectrum; Monochromators using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/001—Optical devices or arrangements for the control of light using movable or deformable optical elements based on interference in an adjustable optical cavity
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting

Definitions

  • the invention relates to a modulator for modulating the Intensity of a light beam according to the generic term of Claim 1.
  • the modulator described is relatively simple in construction and has good modulation properties. However, it is from absolute value of the distance between the fiber end and the Mirror dependent, which is characterized by various influences changed, e.g. depending on the temperature. It must therefore, a controller can be provided that the "optical Distance "keeps constant.
  • the solution mentioned is particularly simple out and works very sensitive. It forms one excellent modulator of the optical class Reflection modulators with movable mirror surfaces.
  • Fig. 1 shows a basic, perspective view of a Modulators 11.
  • the light reaches the arrangement via a Optical fiber 13, e.g. a single mode fiber.
  • Optical fiber 13 e.g. a single mode fiber.
  • the end of Fiber 13 exits the light and expands in a known manner conical and is through a converging lens 16, the there is a focal point at the light exit point 14, parallelized.
  • the light beam now strikes a two-part mirror 19, which is arranged orthogonally to the light beam that each of the Partial mirror 19.1 and 19.2 approximately the same amount of light receives.
  • the incoming light is due to the orthogonality reflected in itself through the converging lens 16 focused and finally back into the optical fiber 13 fed. This is indicated by the double arrow 17.
  • the two partial mirrors 19.1, 19.2 are flat and are in the Hibernation on the same level or on the same level. This creates a gap between the light from the two Partial mirror 19.1, 19.2 is reflected, no Phase difference and the returning light beam is undisturbed.
  • the phase difference is due to a relative movement the two partial mirrors 19.1, 19.2 come about.
  • the Relative movement can be achieved by one partial mirror, e.g. 19.1 is rigidly attached and the other partial mirror 19.2 is moved orthogonally to its mirror surface.
  • both partial mirrors can also be used at the same time moved, e.g. unevenly strong in the same Direction or preferably equally strong in opposite directions.
  • In the latter Fall is sufficient for each partial mirror 19.1, 19.2 by an eighth wavelength of light, from maximum Brightness to minimum brightness or maximum extinction modulate or switch digitally. This means at a common wavelength of e.g. 3100 nm a deflection the partial mirror 19.1, 19.2 by only about 400 nm each.
  • Each partial mirror 19.1, 19.2 should - as already mentioned - the Half of the incoming or outgoing light reflect. If this is not exactly the case, the result is a reduced depth of modulation. However, there is none Dependence on the shape of the mirror. It is therefore possible instead of the plan partial mirrors 19.1, 19.2 shown in FIG linear dividing line 20 the area of a partial mirror to be circular and this partial mirror in Arrange a circular section of the second partial mirror.
  • Fig. 2 shows a greatly enlarged detail view of the Partial mirror 19.1, 19.2.
  • the partial mirrors form two side by side, stretched foils.
  • the tension of the partial mirrors arises under the influence of variable electrostatic forces between the sheets attached to two sides and one adjacent control plate with two control electrodes.
  • the partial mirrors 19.1, 19.2 bend in an arc. It is now advantageous, through a constant, common, electrical Preload the two partial mirrors in the same way mechanically pretension. This will make a stable Basic position of the partial mirrors 19.1, 19.2 reached from which the partial mirrors can be deflected in opposite directions.
  • FIG. 3 shows the section through a further modulator 11.
  • the partial mirrors 19.1, 19.2 are more conscious Deviation from the plane mirror is concave.
  • the center of the optical axis 15 given by the optical fiber 13 arranged inner partial mirror 19.1 forms a spherical cap.
  • the second partial mirror 19.2 has a circular one Recess in which the first partial mirror 19.1 is arranged.
  • Both partial mirrors 19.1, 19.2 complement one another larger spherical cap.
  • the center of this spherical cap lies in the light exit point 14 of the optical fiber 13. In this way, a converging lens 16 corresponding to FIG. 1 omitted since all the light is independent of his Room exit angle always to the light exit point 14 of the fiber 13 is reflected back.
  • Partial mirror (s) 19.1, 19.2 of FIG. 3 can for example solid state elements which can be influenced electrically, which serve the or wear the partial mirror.
  • solid-state elements are especially piezoelectric transducers, e.g. Crystals.
  • the partial mirrors 19.1, 19.2 Fig. 3 similar to those of Fig. 2 as membranes train and by electrostatic forces against one Deflect carrier 22.
  • Such membranes can be passed through targeted etching of doped semiconductors, e.g. Silicon single crystal wafers with suitable pn doping layers, produce relatively easily.
  • Metallic by vapor deposition Layers can then both the mirror properties as well as electrodes for applying the electrostatic Generate tensions that the deflection of the partial mirror 19.1, 19.2 effect. It is therefore possible to be very small and inexpensive to produce compact modulators 11 that extend into the MHz range work reliably. The control of such Modulators 11 only require relatively low voltages and hardly any electricity.
  • FIG. 4 shows, as an alternative to the invention, a third modulator 11 arriving through the converging lens 16 parallelized Light beam not orthogonal to Fig. 1 on the two partial mirrors 19.1, 19.2, but obliquely under one largely freely selectable angle.
  • a second converging lens 26 is required, which the reflected partial beams focused and the entry point 24 supplies a second, outgoing optical fiber 23.
  • this modulator is modulating a continuous Light beam possible, the direction of passage does not matter plays.
  • the type of described Modulation in any case a modulation of the light intensity or the light intensity of a guided in an optical fiber Represents light beam. This modulation can also be more specific viewed as amplitude modulation and e.g. for the purposes of Information transfer can be used.
  • the depth of the Modulation depends on how much light the two Partial mirror 19.1, 19.2 relative to the interference process contribute. Are the two interfering light intensities the same size, then there is a maximum depth of modulation. In contrast, the two interfering light intensities are not the same large, then there is a much smaller one Depth of modulation. It is important in any case that each of the two partial mirrors 19.1, 19.2 a substantial part of the of the optical fiber 13 emerging, total light reflects and then brings to interference.

Description

Die Erfindung betrifft einen Modulator zum Modulieren der Intensität eines Lichtstrahls entsprechend dem Oberbegriff von Anspruch 1.The invention relates to a modulator for modulating the Intensity of a light beam according to the generic term of Claim 1.

Aus der Schrift DE 40 31 970 A1 ist ein optischer Reflexionsmodulator bekannt. Bei diesem trifft das aus dem stumpfen Ende einer Lichtleitfaser austretende Licht auf einen orthogonal zur Faser angeordneten Spiegel. Dieser Spiegel wirft das Licht in sich zurück, wobei in Art eines Fabry-Perot-Resonators eine stehende Welle zwischen dem spiegelnden Faserende und dem Spiegel auftritt, sofern deren Abstand dem Vielfachen einer halben Wellenlänge des verwendeten Lichts entspricht. Durch Verändern des genannten Abstandes, insbesondere durch Verschiebung des Spiegels, lässt sich der Fabry-Perot-Resonator verstimmen und damit die Lichtstärke verändern.From the document DE 40 31 970 A1 is an optical Reflection modulator known. In this, this is from the blunt end of an optical fiber emerging light on you mirror arranged orthogonally to the fiber. That mirror throws the light back into itself, in the manner of a Fabry-Perot resonator a standing wave between the reflecting Fiber end and the mirror occurs, provided that their distance the Multiples of half a wavelength of the light used corresponds. By changing the distance mentioned, especially by shifting the mirror The Fabry-Perot resonator detunes and thus the light intensity change.

Der beschriebene Modulator ist im Aufbau relativ einfach und besitzt gute Modulationseigenschaften. Er ist jedoch vom absoluten Wert des Abstandes zwischen dem Faserende und dem Spiegel abhängig, der sich durch mancherlei Einflüsse verändert, z.B. in Abhängigkeit vom der Temperatur. Es muss daher ein Regler vorgesehen werden, der den "optischen Abstand" konstant hält.The modulator described is relatively simple in construction and has good modulation properties. However, it is from absolute value of the distance between the fiber end and the Mirror dependent, which is characterized by various influences changed, e.g. depending on the temperature. It must therefore, a controller can be provided that the "optical Distance "keeps constant.

Ausgehend von diesem Stand der Technik ist es die Aufgabe der Erfindung, einen Lichtmodulator anzugeben, der vergleichbare Modulationseigenschaften aufweist, jedoch unabhängig von der genannten Problematik einer konstant zu haltenden Länge ist.Based on this state of the art, it is the task of Invention to provide a light modulator that is comparable Has modulation properties, but regardless of the mentioned problem of a constant length is.

Diese Aufgabe wird durch den kennzeichnenden Teil des Anspruchs 1 gelöst. Die abhängigen Ansprüche geben Ausgestaltungen der Erfindung an. This task is carried out by the characteristic part of the Claim 1 solved. Give the dependent claims Embodiments of the invention.

Die genannte Lösung zeichnet sich durch besondere Einfachheit aus und arbeitet sehr empfindlich. Sie bildet damit einen hervorragenden Modulator der Gattung der optischen Reflexionsmodulatoren mit beweglichen Spiegelflächen.The solution mentioned is particularly simple out and works very sensitive. It forms one excellent modulator of the optical class Reflection modulators with movable mirror surfaces.

Im folgenden wird die Erfindung anhand von vier Figuren beispielsweise näher beschrieben. Es zeigen:

  • Fig. 1 - perspektivische, prinzipielle Ansicht eines ersten Modulators,
  • Fig. 2 - vergrösserte Detailansicht von Fig. 1,
  • Fig. 3 - Schnitt durch einen zweiten Modulator,
  • Fig. 4 - Ansicht eines dritten Modulators.
    • The invention is described in more detail below with reference to four figures, for example. Show it:
  • 1 - perspective, basic view of a first modulator,
  • 2 - enlarged detail view of FIG. 1,
  • 3 - section through a second modulator,
  • Fig. 4 - View of a third modulator.

    • Fig. 1 zeigt eine prinzipielle, perspektivische Ansicht eines Modulators 11. Das Licht erreicht die Anordnung über eine Lichtleitfaser 13, z.B. eine Monomode-Glasfaser. Am Ende der Faser 13 tritt das Licht aus, weitet sich in bekannter Weise kegelförmig auf und wird durch eine Sammellinse 16, deren einer Brennpunkt an der Lichtaustrittstelle 14 liegt, parallelisiert. Der relativ breite, parallelisierte Lichtstrahl trifft nun so auf einen zweigeteilten Spiegel 19, der orthogonal zum Lichtstrahl angeordnet ist, dass jeder der Teilspiegel 19.1 und 19.2 etwa die gleiche Lichtmenge empfängt. Durch die Orthogonalität wird das ankommende Licht in sich selbst zurückgespiegelt, durch die Sammellinse 16 fokussiert und schliesslich wieder in die Lichtleitfaser 13 eingespeist. Dies ist durch den Doppelpfeil 17 angedeutet.Fig. 1 shows a basic, perspective view of a Modulators 11. The light reaches the arrangement via a Optical fiber 13, e.g. a single mode fiber. At the end of Fiber 13 exits the light and expands in a known manner conical and is through a converging lens 16, the there is a focal point at the light exit point 14, parallelized. The relatively wide, parallelized one The light beam now strikes a two-part mirror 19, which is arranged orthogonally to the light beam that each of the Partial mirror 19.1 and 19.2 approximately the same amount of light receives. The incoming light is due to the orthogonality reflected in itself through the converging lens 16 focused and finally back into the optical fiber 13 fed. This is indicated by the double arrow 17.

    Die beiden Teilspiegel 19.1, 19.2 sind plan und liegen im Ruhezustand auf gleichem Niveau bzw. in der gleichen Ebene. Hierdurch besteht zwischen dem Licht, das von den beiden Teilspiegeln 19.1, 19.2 reflektiert wird, kein Phasenunterschied und der rücklaufende Lichtstrahl ist ungestört.The two partial mirrors 19.1, 19.2 are flat and are in the Hibernation on the same level or on the same level. This creates a gap between the light from the two Partial mirror 19.1, 19.2 is reflected, no Phase difference and the returning light beam is undisturbed.

    Anders verhält es sich, wenn die beiden Teilspiegel auf unterschiedlichem Niveau liegen. In diesem Fall ergeben sich für die von den beiden Teilspiegeln 19.1, 19.2 reflektierten Teil-Lichtstrahlen unterschiedliche, optische Weglängen. Dies bedeutet, dass eine vom Niveau-Unterschied abhängige Phasendifferenz auftritt, die durch Interferenz den reflektierten Gesamt-Lichtstrahl mehr oder weniger abschwächt und damit moduliert. Hierbei kommt es nicht auf irgendeine absolute Länge an, sondern auf den genannten relativen Niveau-Unterschied und die hierdurch bewirkte Phasendifferenz. Hiermit entfallen alle Störeinflüsse der Umgebung weitgehend. Temperaturschwankungen beispielsweise spielen für die Modulationstiefe keine Rolle.It is different when the two partial mirrors are open different levels. In this case arise for those reflected by the two partial mirrors 19.1, 19.2 Partial light beams have different optical path lengths. This means that one is dependent on the level difference Phase difference occurs by interference reflected overall light beam more or less diminishes and thus modulated. It does not matter absolute length, but on the relative level difference mentioned and the phase difference caused thereby. This largely eliminates all interference from the environment. Temperature fluctuations, for example, play for the Modulation depth doesn't matter.

    Allgemein gilt, dass die Phasendifferenz durch eine Relativ-Bewegung der beiden Teilspiegel 19.1, 19.2 zustande kommt. Die Relativ-Bewegung ist erreichbar, indem der eine Teilspiegel, z.B. 19.1 starr befestigt ist und der andere Teilspiegel 19.2 orthogonal zu seiner Spiegelfläche verschoben wird. Die Richtung vor oder zurück der Verschiebung spielt dabei keine Rolle. Es können jedoch auch beide Teilspiegel gleichzeitig verschoben werden, z.B. ungleichmässig stark in die gleiche Richtung oder bevorzugt gleich stark gegensinnig. Im letzteren Fall genügt für jeden Teilspiegel 19.1, 19.2 eine Verschiebung um eine achtel Wellenlänge des Lichts, um von maximaler Helligkeit auf minimale Helligkeit bzw. maximale Auslöschung durchzumodulieren bzw. digital umzuschalten. Dies bedeutet bei einer üblichen Wellenlänge von z.B. 3100 nm eine Auslenkung der Teilspiegel 19.1, 19.2 um jeweils nur etwa 400 nm.In general, the phase difference is due to a relative movement the two partial mirrors 19.1, 19.2 come about. The Relative movement can be achieved by one partial mirror, e.g. 19.1 is rigidly attached and the other partial mirror 19.2 is moved orthogonally to its mirror surface. The There is no direction forwards or backwards of the shift Role. However, both partial mirrors can also be used at the same time moved, e.g. unevenly strong in the same Direction or preferably equally strong in opposite directions. In the latter Fall is sufficient for each partial mirror 19.1, 19.2 by an eighth wavelength of light, from maximum Brightness to minimum brightness or maximum extinction modulate or switch digitally. This means at a common wavelength of e.g. 3100 nm a deflection the partial mirror 19.1, 19.2 by only about 400 nm each.

    Jeder Teilspiegel 19.1, 19.2 sollte - wie bereits erwähnt - die Hälfte des ankommenden bzw. abgehenden Lichts reflektieren. Ist dies nicht exakt der Fall, dann ergibt sich eine reduzierte Modulationstiefe. Hierbei besteht jedoch keine Abhängigkeit von der Spiegelform. Es ist daher möglich, statt der in Fig. 1 gezeigten planen Teilspiegel 19.1, 19.2 mit linearer Trennungslinie 20 die Fläche des einen Teilspiegels kreisförmig auszubilden und diesen Teilspiegel im Kreisausschnitt des zweiten Teilspiegels anzuordnen. Each partial mirror 19.1, 19.2 should - as already mentioned - the Half of the incoming or outgoing light reflect. If this is not exactly the case, the result is a reduced depth of modulation. However, there is none Dependence on the shape of the mirror. It is therefore possible instead of the plan partial mirrors 19.1, 19.2 shown in FIG linear dividing line 20 the area of a partial mirror to be circular and this partial mirror in Arrange a circular section of the second partial mirror.

    Fig. 2 zeigt eine stark vergrösserte Detailansicht der Teilspiegel 19.1, 19.2. In dieser bevorzugten Ausführungsart bilden die Teilspiegel zwei nebeneinander angeordnete, gespannte Folien. Die Spannung der Teilspiegel entsteht unter dem Einfluss von variierbaren elektrostatischen Kräften zwischen den an zwei Seiten befestigten Folien und einer benachbarten Steuerplatte mit zwei Steuerelektroden. Beim Anlegen einer elektrischen Spannung zwischen einer Leitschicht der Teilspiegel 19.1, 19.2, insbesondere der aufgedampften, metallischen Spiegelschicht, und den Steuerelektroden, verbiegen sich die Teilspiegel 19.1, 19.2 bogenförmig. Es ist nun vorteilhaft, durch eine konstante, gemeinsame, elektrische Vorspannung die beiden Teilspiegel in gleicher Weise mechanisch vorzuspannen. Hiermit wird eine stabile Grundstellung der Teilspiegel 19.1, 19.2 erreicht, von der aus sich die Teilspiegel gegensinnig auslenken lassen. Hierzu ist z.B. eine gemeinsame Steuerspannung für die beiden Teilspiegel 19.1, 19.2 gegensinnig der elektrischen Vorspannung zu überlagern. Hierbei sind - wie erwähnt - nur sehr geringe mechanische Auslenkungen in die eine bzw. in die andere Richtung für eine digitale Umsteuerung "hell/dunkel" erforderlich.Fig. 2 shows a greatly enlarged detail view of the Partial mirror 19.1, 19.2. In this preferred embodiment the partial mirrors form two side by side, stretched foils. The tension of the partial mirrors arises under the influence of variable electrostatic forces between the sheets attached to two sides and one adjacent control plate with two control electrodes. At the Applying an electrical voltage between a conductive layer the partial mirror 19.1, 19.2, in particular the vapor-deposited, metallic mirror layer, and the control electrodes, the partial mirrors 19.1, 19.2 bend in an arc. It is now advantageous, through a constant, common, electrical Preload the two partial mirrors in the same way mechanically pretension. This will make a stable Basic position of the partial mirrors 19.1, 19.2 reached from which the partial mirrors can be deflected in opposite directions. This is e.g. a common control voltage for the two partial mirrors 19.1, 19.2 in opposite directions to the electrical bias overlay. As mentioned, there are only very few mechanical deflections in one or the other Direction for a digital changeover "light / dark" required.

    Die Forderung nach planen Teilspiegeln 19.1, 19.2 ist bei der Version entsprechend Fig. 2 nicht vollständig gegeben. Die Teilspiegel dieser Ausführungsform sind vielmehr - wie beschrieben - leicht bogenförmig ausgebildet. Wird keine optische Korrektur vorgenommen, dann hat dies natürlich gewisse Einflüsse auf das Interferenzverhalten zwischen den beiden reflektierten Teil-Lichtstrahlen. Diese Einflüsse wirken jedoch nicht in grundsätzlicher Art. Das Gesamtverhalten des Modulators 11 bleibt vielmehr voll erhalten.The demand for plan partial mirrors 19.1, 19.2 is with Version according to Fig. 2 not completely given. The Rather, partial mirrors of this embodiment are - like described - slightly arched. Will not made optical correction, then of course this has certain influences on the interference behavior between the two reflected partial light beams. These influences however, do not work in a fundamental way Rather, the overall behavior of the modulator 11 remains full receive.

    Fig. 3 zeigt den Schnitt durch einen weiteren Modulator 11. Bei diesem sind die Teilspiegel 19.1, 19.2 in bewusster Abweichung vom Planspiegel konkav gebogen. Der zentrisch zur durch die Lichtleitfaser 13 gegebenen optischen Achse 15 angeordnete innere Teilspiegel 19.1 bildet eine Kugelkalotte. Der zweite Teilspiegel 19.2 besitzt eine kreisförmige Ausnehmung, in der der erste Teilspiegel 19.1 angeordnet ist. Beide Teilspiegel 19.1, 19.2 ergänzen einander zu einer grösseren Kugelkalotte. Der Mittelpunkt dieser Kugelkalotte liegt in der Lichtaustrittstelle 14 der Lichtleitfaser 13. Hierdurch kann eine Sammellinse 16 entsprechend Fig. 1 entfallen, da das gesamte Licht unabhängig von seinem Raumaustrittswinkel stets zur Lichtaustrittstelle 14 der Faser 13 zurückreflektiert wird.3 shows the section through a further modulator 11. In this, the partial mirrors 19.1, 19.2 are more conscious Deviation from the plane mirror is concave. The center of the optical axis 15 given by the optical fiber 13 arranged inner partial mirror 19.1 forms a spherical cap. The second partial mirror 19.2 has a circular one Recess in which the first partial mirror 19.1 is arranged. Both partial mirrors 19.1, 19.2 complement one another larger spherical cap. The center of this spherical cap lies in the light exit point 14 of the optical fiber 13. In this way, a converging lens 16 corresponding to FIG. 1 omitted since all the light is independent of his Room exit angle always to the light exit point 14 of the fiber 13 is reflected back.

    Als Antrieb für die Linearbewegung des einen oder der beiden Teilspiegel(s) 19.1, 19.2 von Fig. 3 können beispielsweise elektrisch beeinflussbare Festkörperelemente dienen, die den bzw. die Teilspiegel tragen. Solche Festkörperelemente sind vor allem piezoelektrische Wandler, z.B. Quarze.As a drive for the linear movement of one or both Partial mirror (s) 19.1, 19.2 of FIG. 3 can for example solid state elements which can be influenced electrically, which serve the or wear the partial mirror. Such solid-state elements are especially piezoelectric transducers, e.g. Crystals.

    Es ist jedoch auch möglich, die Teilspiegel 19.1, 19.2 von Fig. 3 ähnlich wie diejenigen von Fig. 2 als Membranen auszubilden und durch elektrostatische Kräfte gegenüber einem Träger 22 auszulenken. Derartige Membranen lassen sich durch gezieltes Ätzen von dotierten Halbleitern, z.B. Silizium-Einkristall-Scheiben mit geeigneten pn-Dotierungsschichten, relativ problemlos herstellen. Durch Aufdampfen metallischer Schichten lassen sich sodann sowohl die Spiegeleigenschaften als auch Elektroden zum Anlegen der elektrostatischen Spannungen erzeugen, die die Auslenkung der Teilspiegel 19.1, 19.2 bewirken. Es ist damit preiswert möglich, sehr kleine und kompakte Modulatoren 11 herzustellen, die bis in den MHz-Bereich zuverlässig arbeiten. Die Ansteuerung solcher Modulatoren 11 erfordert nur relativ niedrige Spannungen und kaum Strom.However, it is also possible to use the partial mirrors 19.1, 19.2 Fig. 3 similar to those of Fig. 2 as membranes train and by electrostatic forces against one Deflect carrier 22. Such membranes can be passed through targeted etching of doped semiconductors, e.g. Silicon single crystal wafers with suitable pn doping layers, produce relatively easily. Metallic by vapor deposition Layers can then both the mirror properties as well as electrodes for applying the electrostatic Generate tensions that the deflection of the partial mirror 19.1, 19.2 effect. It is therefore possible to be very small and inexpensive to produce compact modulators 11 that extend into the MHz range work reliably. The control of such Modulators 11 only require relatively low voltages and hardly any electricity.

    Fig. 4 zeigt ald Alternative zur Erfindung einen dritten Modulator 11. Bei diesem trifft der durch die Sammellinse 16 parallelisierte, ankommende Lichtstrahl nicht entsprechend Fig. 1 orthogonal auf die beiden Teilspiegel 19.1, 19.2 auf, sondern schräg unter einem weitgehend frei wählbaren Winkel. Bei diesem dritten Modulator 11 ist eine zweite Sammellinse 26 erforderlich, die die reflektierten Teilstrahlen fokussiert und der Eintrittstelle 24 einer zweiten, abgehenden Lichtleitfaser 23 zuführt. Mit diesem Modulator ist das Modulieren eines durchgehenden Lichtstrahls möglich, wobei die Durchgangsrichtung keine Rolle spielt.4 shows, as an alternative to the invention, a third modulator 11 arriving through the converging lens 16 parallelized Light beam not orthogonal to Fig. 1 on the two partial mirrors 19.1, 19.2, but obliquely under one largely freely selectable angle. With this third modulator 11, a second converging lens 26 is required, which the reflected partial beams focused and the entry point 24 supplies a second, outgoing optical fiber 23. With this modulator is modulating a continuous Light beam possible, the direction of passage does not matter plays.

    Neben den beschriebenen gibt es eine ganze Reihe weiterer Varianten, von denen nachfolgend einige erwähnt seien:

    • Die Sammellinsen 16 und 26 können durch andere optische Mittel ersetzt sein, die die gleiche Wirkung haben, z.B. durch Linsensätze oder sphärische Spiegel.
    • Der anhand von Fig. 3 beschriebene Modulator 11 kann in einer Alternative zur Erfindung so abgeändert werden, dass statt des Zurückreflektierens in die eine Lichtleitfaser 13 das reflektierte Licht einer zweiten Lichtleitfaser 23 zugeführt wird. In diesem Fall ergibt sich eine zweite Anordnung zum Modulieren eines durchgehenden Lichtstrahls.
    • Es ist vorteilhaft, die beiden Teilspiegel 19.1, 19.2 in einer gemeinsamen Ebene anzuordnen. Es ist jedoch auch möglich, erheblich unterschiedliche Ebenen vorzusehen.
    In addition to those described, there are a number of other variants, some of which are mentioned below:
    • The converging lenses 16 and 26 can be replaced by other optical means which have the same effect, for example by lens sets or spherical mirrors.
    • The modulator 11 described with reference to FIG. 3 can be modified in an alternative to the invention so that instead of reflecting back into the one optical fiber 13, the reflected light is fed to a second optical fiber 23. In this case, there is a second arrangement for modulating a continuous light beam.
    • It is advantageous to arrange the two partial mirrors 19.1, 19.2 in a common plane. However, it is also possible to provide significantly different levels.

    Zum Schluss sei noch erwähnt, dass die Art der beschriebenen Modulation in jedem Fall eine Modulation der Lichtintensität bzw. der Lichtstärke eines in einer Optikfaser geführten Lichtstrahls darstellt. Diese Modulation kann spezieller auch als Amplitudenmodulation angesehen und z.B. für Zwecke der Informationsübertragung verwendet werden. Die Tiefe der Modulation hängt dabei davon ab, wieviel Licht die beiden Teilspiegel 19.1, 19.2 relativ zum Interferenzprozess beisteuern. Sind die beiden interferierenden Lichtstärken gleich gross, dann ergibt sich eine maximale Modulationstiefe. Sind die beiden interferierenden Lichtstärken dagegen ungleich gross, dann ergibt sich eine deutlich geringere Modulationstiefe. Wichtig ist auf alle Fälle, dass jeder der beiden Teilspiegel 19.1, 19.2 einen wesentlichen Teil des aus der Lichtleitfaser 13 austretenden, gesamten Lichts reflektiert und anschliessend zur Interferenz bringt.Finally, it should be mentioned that the type of described Modulation in any case a modulation of the light intensity or the light intensity of a guided in an optical fiber Represents light beam. This modulation can also be more specific viewed as amplitude modulation and e.g. for the purposes of Information transfer can be used. The depth of the Modulation depends on how much light the two Partial mirror 19.1, 19.2 relative to the interference process contribute. Are the two interfering light intensities the same size, then there is a maximum depth of modulation. In contrast, the two interfering light intensities are not the same large, then there is a much smaller one Depth of modulation. It is important in any case that each of the two partial mirrors 19.1, 19.2 a substantial part of the of the optical fiber 13 emerging, total light reflects and then brings to interference.

    Claims (5)

    1. Modulator (11) for modulating the intensity of a free light beam which exits and reenters an optical fibre (13), comprising
      a mirror composed of two partial mirrors (19.1, 19.2),
      means allowing to direct approximately equal parts of the free light beam onto the two partial mirrors (19.1, 19.2), and
      a drive for the controlled electromechanical movement of the two partial mirrors (19.1, 19.2) relative to each other in order to produce two optical paths of different lengths,
      characterised in that
      a single optical fibre (13) is provided from which the free light beam exits and into which it reenters,
      the means for dividing the free light beams are so designed that the latter is spread on a relatively large surface when impinging on the partial mirrors (19.1, 19.2) and
      the partial mirrors (19.1, 19.2) are so designed and positioned that all of the impinging light is reflected onto itself.
    2. Modulator according to claim 1,
      characterised in that
      the front surface of the optical fibre (13) is surface-ground orthogonally to the longitudinal direction of the fibre,
      the two partial mirrors (19.1, 19.2) are essentially plane,
      optical means for collimating the divergent light beam emerging from the optical fibre (13) are interposed between the optical fibre (13) and the partial mirrors (19.1, 19.2),
      one of the focal points of these optical means is located at the light exit point (14) of the optical fibre, and in that
      the collimated light impinges on the mirrors (19.1, 19.2) essentially orthogonally.
    3. Modulator according to claim 2,
      characterised in that
      the optical means are in the form of a focusing lens (16).
    4. Modulator according to claim 2,
      characterised in that
      the front surface of the optical fibre (13) is surface-ground orthogonally to the longitudinal direction of the fibre,
      one of the partial mirrors (19.1) is disposed in a circular recess of the second partial mirror (19.2),
      both partial mirrors are concave in such a manner that together they essentially form a spherical section whose section axis is common to both mirrors, and in that
      the centre of the spherical section is located at the light exit point (14) of the optical fibre (13).
    5. Modulator according to claim 1,
      characterised in that
      the partial mirrors (19.1, 19.2) are in the form of vacuum-evaporated diaphragms,
      at least one support (22) is associated to the diaphragms, and in that
      electric control voltages are applicable between the diaphragms and the supports (22).
    EP93203160A 1992-11-20 1993-11-12 Light modulator Expired - Lifetime EP0599375B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    CH3566/92 1992-11-20
    CH356692 1992-11-20

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    EP0599375A1 EP0599375A1 (en) 1994-06-01
    EP0599375B1 true EP0599375B1 (en) 1999-03-03

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    Application Number Title Priority Date Filing Date
    EP93203160A Expired - Lifetime EP0599375B1 (en) 1992-11-20 1993-11-12 Light modulator

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    US (1) US5508840A (en)
    EP (1) EP0599375B1 (en)
    DE (1) DE59309409D1 (en)

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    EP0599375A1 (en) 1994-06-01
    US5508840A (en) 1996-04-16
    DE59309409D1 (en) 1999-04-08

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